1. Field of the Invention
The present invention relates to a clad plate (referred to below as a “parallelly joined clad plate”) that joins together an aluminum plate made of an aluminum material and a hard metal plate made of a copper material, or other suitable material, at the respective side end surfaces (end surfaces in the width direction) thereof.
2. Description of the Related Art
In lithium ion battery packs that are installed in hybrid vehicles and in various types of electronic devices, lithium ion batteries are connected in series as needed, and these groups of serially connected batteries are connected in parallel. For this reason, many wiring materials have been used for connecting the batteries. Lithium ion batteries have positive terminals that are made from an aluminum material and negative terminals that are mainly made from a copper material. For this reason, wiring material for connecting positive terminals and negative terminals in series is preferably a composite metal material, with one end made of an aluminum material and the other end made of a metal material having good electrical conductivity, such as a copper material.
The inventors of the present invention have previously offered a parallelly joined clad plate suitable for this type of composite metal material in Japanese Laid-open Patent Publication No. 2008-6496.This parallelly joined clad plate is joined by pressure welding at the respective side end surfaces of a first metal plate made of an aluminum material and a second metal plate made of a metal material such as copper material. A ridge and a groove are formed from the front end side to the rear end side of the side surface of the first metal plate, a ridge and a groove are also formed from the front end side to the rear end side of the side surface of the second metal plate, and the side end surfaces are jointed together in a condition in which the ridge of the first metal plate is engaged to the groove of the second metal plate, and the groove of the first metal plate is engaged to the ridge of the second metal plate, respectively. In this parallelly joined clad plate, joined surfaces (side end surfaces) are jointed together by pressure welding, with the ridges and grooves being engaged each other. Accordingly, good joining is produced.
In the case of wiring materials for electronic components and battery packs installed in vehicles, electric tools and the like, durability and reliability are recently desired in service environments that are extreme in terms of vibration and shock. Moreover, battery connection configurations are becoming more complicated, and there are situations in which wiring materials must be worked by bending, so that separation-resistant characteristics against bending are also desired.
On the other hand, a clad plate produced by pressure welding and diffusion joining of an aluminum plate and a copper plate along the plate surfaces thereof has been proposed in Japanese Laid-open Patent Publication No. 11-156995.In this clad plate, the aluminum plate and the copper plate are joined in an integral manner via a nickel layer to improve the joint strength between the aluminum plate and the copper plate.
The inventors of the present invention, in order to additionally improve the joint strength between the joined surfaces in a parallelly joined clad plate joined by the pressure welding of an aluminum plate and a copper plate at the respective side end surfaces thereof, produced a parallelly joined clad material in which the side end surface of an aluminum plate and the side end surface of a copper plate are joined together by pressure welding and diffusion joining with a nickel layer provided therebetween. It was confirmed that the joint strength of the parallelly joined clad plate is increased by providing the nickel layer. However, the front end portion of the side end surface of the copper plate and the nickel layer adjacent thereto is not sufficiently press-welded to the rear end portion of the side end surface of the aluminum plate, so that sufficient joint strength is not obtained. As a result, when the parallelly joined clad plate has been worked by bending, with the front end portion of the copper plate positioned towards the outside of the bend section, there is a tendency for the front end portion of the copper plate and the nickel layer adjacent thereto to undesirably peel off from the rear end portion of the aluminum plate.